The present invention relates in general to automotive heating, ventilating, and air conditioning (HVAC) systems, and, more specifically, to an air inlet system for selectably supplying a blower with fresh air, recirculated air, or a blend of fresh and recirculated air.
An air inlet mechanism of a typical HVAC system is used to control the blend of inflowing air from two air source passages into the blower for passing the air across one or more heat exchangers before distributing it to the passenger compartment. Fresh outside air is available from one air source passage and recirculated cabin air is available from the other. The inlet mechanism settings determine the mix of air coming from each source. Each setting is referred to as a mode. The modes may include 1) fully recirculated, 2) fresh and recirculated combined (otherwise known as blend), 3) fully fresh, and 4) Fresh Restricted.
Conventional inlet mechanisms employ movable doors or dampers. Implementing fully recirculated and fully fresh modes is typically achieved using a single door. The Blend mode can be implemented by moving the single door to an intermediate position at which air can enter the HVAC via both air source passages. By blending the air sources in the Blend mode, a desired temperature effect can be obtained.
In modern vehicles with smaller, more efficient engines designed to meet increased fuel economy requirements, it has become more difficult to meet heater and defrost performance criteria. Blend strategies address this issue by harnessing the energy savings associated with the recirculation of conditioned air from the cabin, while ensuring access to sufficient fresh air to avoid fogging.
A significant disadvantage of conventional single door blend systems is that as the vehicle speed increases, a ram air effect can force unconditioned air from the fresh air passage into the cabin via the recirculated air passage. One solution to this problem entails the use of a second door positioned in the fresh air stream to mitigate the ram air effect. The second door also permits the overall flow of air in the fully fresh mode to be controlled at higher vehicle speeds. Disadvantages include the cost of the second door and its actuator as well as increased noise since the incoming fresh air passes through two openings. Added components can also result in moving parts that generate additional squeaks, rattles, and scrapes.
It would be desirable to construct an air inlet mechanism using a single door that would include all four modes mentioned above that does not allow leakage of unconditioned air into the cabin, that allows the overall flow of air in the HVAC to be controlled at higher vehicle speeds, and that avoids additional squeaks, rattles, and scrapes.